In a Passive Optical Network (PON), optical fibers are deployed in a central split or dual split branch arrangement in order to distribute signals from the OLT (Optical Line Transmitters) in the central office towards a plurality of ONU's at the subscriber's residence. In order to identify failures in the network that need to be restored when a subscriber lacks service, optical time domain reflectometry (OTDR) is used. For a distributed split PON, this method is inappropriate since OTDR measurements carried out from the central office cannot distinguish between the superpostition of the back reflected signals from the splitter branches. Consequently, it is not possible to locate the fault after the split branch. As a result, field technicians (technicians that have to go into the field equipped with an OTDR) are necessary to do measurements after the split branch to identify possible failures.
The negative drawbacks of this approach are (1) that it is a very expensive method that cannot be used to measure the network pro-actively on a regular basis; and (2) that for field technician measurements, connectors are needed in the outside plant in order to allow for connecting the OTDR equipment to the cable infrastructure. This can lead to connector failures over time in case cleaning precautions have not been taken into account by the field technician crews. In addition, the lifetime of the network elements where the monitoring has to be carried out is fairly reduced due to a substantial number of re-entrances in the network element. Known systems are described, for example, in U.S. Pat. No. 6,396,575 of W. R. Holland (Lucent), U.S. Pat. No. 6,771,358 of M. Shigeghara and H. Kanomori (Sumitomo), and U.S. Reissue Pat. 36471 of L. G. Cohen (Lucent).